Use of the average electromyogram in design evaluation Investigation of a whole-body task

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Abstract
The information content of the average electromyogram (AEMG) was investigated in a whole-body task, load carriage. Four subjects walked for approximately 2 hours at 5-6km/h with each of three different loads (20, 25 or 32 kg) in each of two placements on the back. EMG was sampled for 15 strides after 5, 37 and 97min walking. The myoelectric signal was telemetered from the tibialis anterior, vastus lateralis, biceps femoris, erector spinae and trapezius muscles, then processed digitally to yield the time average of the rectified electromyogram (AEMG). Analyses of variance indicated a significant load magnitude by load placement by duration interaction on the trapezius muscle. The 20 kg load tended to elicit more EMG from trapezius than the other two over the entire duration of load carriage, but only for the high load placement. In the low placement all three loads elicited similar AEMG values from trapezius after 97min load carriage. Subjects responded quite differently to the independent variables, but all showed appreciable EMG changes in several of the experimental conditions. Individual differences, important in work task assessments, tended to be masked by examining group means alone. The results indicate that AEMG measures do provide useful information in the investigation of whole-body tasks, but that their use is less straightforward in this capacity than in the investigation of more constrained or simplified tasks.